I want to mod my ECB to dump smoke through the rotisserie hole in my grill.

Hi! I have an ECB with some mods that I found on here a long time ago, but I don't use it too much - I had a hard time using it. It occurred to me that instead of trying to regulate the temperature in the smoker, and instead of buying a new expensive offset smoker/grill combo deal, I should just drill a hole in the top of ECB, stick some ventilation ducting on it and vent it straight into the rotisserie hole in my grill. Then I'll have coldish smoke I hope and I could regulate the temperature with the regular grill (I have a natural gas grill).

So: First question:

Is this a terrible idea? I was thinking of sticking a little PC case fan (like http://ftaelectronics.ca/store/120mm-internal-desktop-pc-fan-for-computer-case-cooling.html or similar) somewhere in between the ECB and the grill to push the smoke into the grill. The grill has a fairly large venting gap between the lid and the main body for smoke the escape from. I suppose I could block it if I needed but I don't know if there's a safety issue or anything like that with plugging up all the exits from a natural gas grill. I guess it wouldn't end up 100% airtight anyway..

Main build questions:

I don't know anything about working with metal and ducting and stuff. I'm usually a saw and wood or dremelling plastic kind of guy, so I'm totally lost here. I went by home depot and apparently they don't make ventilation ducts smaller than 3" diameter or so. The rotisserie hole in my grill is quite small at 7/8" diameter. Can anybody recommend what kind of materials I should be using and where I could get it? They sell aluminum sheets but I don't think rolling my own venting ducts is a good idea or even possible for me to do, hah. Also, even if I was able to find the right size duct, at some point I need to get it to a square cross section of an exact size (to fit the case fan), and I guess I have no idea how to fabricate something like that. Disposable lasagna pan/cookie sheet from the grocery store, cut and folded and stapled to make a square box? I don't even know how you're supposed to stick two pieces of metal together like this - staples? Fold it cleverly so it holds itself together? Do I need a torch to braze it?

Sorry for the dumb questions - I'm just totally out of my element here. I don't have welding equipment, metal bending tools, etc. and no experience with this kind of thing.

Also, sorry if this is the wrong forum for this kind of question - if there's a better "I suck at using tools to make stuff" forum you know about, please let me know!